Sheet feeding device and image forming apparatus

ABSTRACT

Provided are a sheet feeding device and an image forming apparatus which can separately feed a sheet with safety without causing the length of an adsorption member to be increased. One end of a flexible adsorption member ( 29 ) is fixed to a holding member ( 24 ) which is disposed on the upper side of a storing unit to store the sheet and rotated in a sheet feeding direction. Then, when the holding member ( 24 ) is rotated, the rigidity of a second region ( 29   b ) of the adsorption member ( 29 ) is set to be lower than that of a first region ( 29   a ) of the adsorption member ( 29 ) which comes into surface contact with the sheet stored in the storing unit and adsorbs the sheet by an adsorbing force by static electricity.

TECHNICAL FIELD

The present invention relates to a sheet feeding device and an image forming apparatus, and particularly to a device that feeds a sheet using an electrostatic adsorbing force.

BACKGROUND ART

An image forming apparatus such as a copying machine or a printer in the related art is provided with a sheet feeding device which feeds a sheet such as plain paper, coated paper, or OHP paper. In general, the image forming apparatus conveys the sheet fed by the sheet feeding device to the image forming section to form an image on the sheet. As such a sheet feeding device, there are a friction feeding method in which the uppermost sheet is separately fed out of a cassette loaded with a sheet bundle using a friction force of a feeding roller, and an air feeding method which adsorbs and conveys the sheet using the air.

By the way, in recent years, noise damping is required in the sheet feeding device, and it is important that the operation sound is suppressed as low as possible. However, in the sheet feeding device using the friction force by the feeding roller, there occurs screechy noises between the sheet and the roller or between the sheets. Further, in the air feeding method, the apparatus is increased in size so that the operation sound is also increased.

As a feeding method receiving the attention in recent years, there is an electrostatic adsorption method in which the sheet is adsorbed using static electricity and conveyed. Further, according to the electrostatic adsorption method, the sheet can be fed without using the friction force, so that it is advantageous for the sound damping. As a sheet feeding device of such an electrostatic adsorption method, the sheet is adsorbed to an adsorption member having an electrostatic adsorption function, and then the adsorption member horizontally moves to convey the sheet (see Patent Literature 1).

CITATION LIST Patent Literature

-   Patent Literature 1: Japanese Patent Laid-Open No. 6-40583

SUMMARY OF INVENTION Technical Problem

Herein, in a case where an adsorption member adsorbing the sheet is configured to be horizontally moved likely to the sheet feeding device disclosed in a conventional electrostatic adsorption method, there is a need to widen a surface contact area between the adsorption member and an uppermost sheet in order to securely separate the sheet. However, in order to widen the surface contact area, the length of the adsorption member is necessarily increased. Further, when the length of the adsorption member is increased, the apparatus is increased in size.

The invention has been made in view of the circumstances, and an object thereof is to provide a sheet feeding device and an image forming apparatus which can separate and feed the sheet with safety without causing the length of the adsorption member to be increased.

Solution to Problem

The invention provides a sheet feeding device which includes a loading portion configured to be loaded with a sheet, a rotation member configured to be disposed on an upper side of the loading portion, and an adsorption member configured to have ends and to be provided such that a part of the adsorption member is fixed to the rotation member and the sheet loaded on the loading portion is electrically adsorbed. The adsorption member includes an adsorption portion which comes into contact with the sheet loaded on the loading portion, and a support portion which is provided at a position near the rotation member from the adsorption portion and has a rigidity lower than that of the adsorption portion with respect to a force applied from a sheet feeding direction.

Advantageous Effects of Invention

According to the invention, a flexible adsorption member is configured such that a rigidity of a fixed portion of the adsorption member is lower than that of an adsorption portion of the adsorption member where a sheet is adsorbed, so that the sheet can be separated and fed with safety without causing the length of the adsorption member to be increased.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating the entire configuration of a full-color laser beam printer as an example of an image forming apparatus provided with a sheet feeding device according to a first embodiment of the invention.

FIG. 2 is a diagram for describing a configuration of the sheet feeding device.

FIG. 3 is a diagram for describing a configuration of an adsorbing and feeding section of the sheet feeding device.

FIG. 4 is a cross-sectional diagram schematically illustrating an adsorption member included in the adsorbing and feeding section.

FIG. 5 is a diagram for describing the bending at the time of a cantilever state of the adsorption member.

FIG. 6 is a diagram for describing a configuration of the adsorption member.

FIG. 7 is a diagram for describing another configuration of the adsorption member.

FIG. 8 is a diagram for describing the bending at the time of the cantilever sate of the adsorption member.

FIG. 9 is a control block diagram of the full-color laser beam printer.

FIG. 10 is a diagram for describing a sheet separating and feeding operation of the sheet feeding device.

FIG. 11 is a flowchart of the sheet separating and feeding operation of the sheet feeding device.

FIG. 12 is a timing chart of the sheet separating and feeding operation of the sheet feeding device.

FIG. 13 is a diagram for comparing the adsorption member with a conventional adsorption member at the time of the sheet separating and feeding operation.

FIG. 14 is a diagram for describing the adsorption member of a sheet feeding device according to a second embodiment of the invention.

FIG. 15 is a diagram for describing the adsorption member of a sheet feeding device according to a third embodiment of the invention.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the invention will be described in detail using the drawings. FIG. 1 is a diagram illustrating the entire configuration of a full-color laser beam printer as an example of an image forming apparatus provided with a sheet feeding device according to a first embodiment of the invention. In FIG. 1, a full-color laser beam printer 100 and a full-color laser beam printer body 100A (hereinafter, referred to as a printer body) are illustrated. The printer body 100A serving as a main body includes the image forming section 100B which forms an image on a sheet such as a recording sheet, a plastic sheet, or cloth, and a sheet feeding device 200 which feeds the sheet.

The image forming section 100B includes process cartridges 7 (7Y, 7M, 7C, and 7K) which form toner images of four colors (yellow, magenta, cyan, and black). Further, the process cartridges 7 include photosensitive drums 1 (1Y, 1M, 1C, and 1K) which serve as image bearing members rotatably driven by a driving unit (a driving source; not illustrated) in a direction of arrow A (a counterclockwise direction), and is mounted to be detachably attachable to the printer body 100A.

In addition, the image forming section 100B includes a scanner unit 3 which is disposed on the upper side of the process cartridges 7 in a vertical direction, irradiates the photosensitive drums 1 with laser beams based on image information, and forms electrostatic latent images on the photosensitive drums 1. Further, the process cartridges 7 includes, besides the photosensitive drums 1, developing units 4 (4Y, 4M, 4C, and 4K) which attach toner to the electrostatic latent images to visualize the latent images, and charging rollers 2 (2Y, 2M, 2C, and 2K) which evenly charge the surfaces of the photosensitive drums.

In addition, the image forming section 100B includes an intermediate transfer belt unit 100C, a secondary transfer portion N2, and a fixing portion 10. The intermediate transfer belt unit 100C includes an endless intermediate transfer belt 5, and primary transfer rollers 8 (8Y, 8M, 8C, and 8K) which are disposed inside the intermediate transfer belt 5 to face the photosensitive drums 1. The intermediate transfer belt 5 rotates in a direction of arrow B while abutting on all the photosensitive drums 1 and suspending on a drive roller 16, a secondary transfer counter roller 17, and a driven roller 18.

Herein, the primary transfer rollers 8 presses the intermediate transfer belt 5 toward the photosensitive drum 1, forms a primary transfer portion N1 which abuts on the intermediate transfer belt 5 and the photosensitive drum 1, and applies a transfer bias to the intermediate transfer belt 5 by a bias applying unit (not illustrated). Then, a primary transfer bias is applied to the intermediate transfer belt 5 by the primary transfer rollers 8, and the respective color toner images on the photosensitive drums are sequentially transferred onto the intermediate transfer belt 5, thereby forming a full-color image on the intermediate transfer belt.

In addition, the secondary transfer roller 9 is disposed at a position facing the secondary transfer counter roller 17 on an outer peripheral surface of the intermediate transfer belt 5, and comes in press contact with the secondary transfer counter roller 17 through the intermediate transfer belt 5 to form the secondary transfer portion N2. Then, the toner images on the intermediate transfer belt 5 are transferred onto a sheet P (the secondary transfer) by applying a bias having an opposite-polarity with respect to a normal charge polarity of the toner from a secondary transfer bias power source (a high-voltage power source) serving as a secondary transfer bias applying unit (not illustrated) to the secondary transfer roller 9.

The sheet feeding device 200 includes a sheet feeding cassette 20 serving as a storing unit which is mounted to be detachably attachable to the printer body 100A, and an adsorbing and feeding section 12 which adsorbs a plurality of sheets P stored in the sheet feeding cassette 20 and feeds the sheets. Then, when the sheet P stored in the sheet feeding cassette 20 is fed, the sheet P is adsorbed by the adsorbing and feeding section 12 and fed out.

Next, an image forming operation of the full-color laser beam printer 100 having such a configuration will be described. When an image reading apparatus (not illustrated) connected to the printer body 100A, or an image signal from a host machine such as a personal computer is input to the scanner unit 3, the photosensitive drum is irradiated with the laser beam corresponding to the image signal from the scanner unit 3. At this time, the surfaces of the photosensitive drums 1 are evenly charged with a polarity and a voltage determined in advance by the charging rollers 2. The electrostatic latent images are formed on the surfaces by irradiating with the laser beams from the scanner unit 3. Thereafter, the electrostatic latent images are developed and visualized by the developing units 4.

For example, first, the photosensitive drum 1Y is irradiated with the laser beam by the image signal of a yellow component from the scanner unit 3, and a yellow electrostatic latent image is formed in the photosensitive drum. Then, the yellow electrostatic latent image is developed by the yellow toner from the developing unit 4Y, and visualizes the latent image into a yellow toner image. Thereafter, the toner image reaches the primary transfer portion N1 where the photosensitive drum 1Y and the intermediate transfer belt 5 abut on each other according to the rotation of the photosensitive drum 1Y. Then, the yellow toner image on the photosensitive drum is transferred onto the intermediate transfer belt in the primary transfer portion N1 by the primary transfer bias applied to the primary transfer roller 8Y.

Next, when a portion carrying with the yellow toner image of the intermediate transfer belt 5 moves, a magenta toner image formed on the photosensitive drum 1M is transferred from above the yellow toner image to the intermediate transfer belt 5 by the method similar to the above description until this stage. Similarly, a cyan toner image and a black toner image are transferred onto the yellow toner image and the magenta toner image in an overlapping manner in the respective primary transfer portions as the intermediate transfer belt 5 moves. Therefore, a full-color toner image is formed on the intermediate transfer belt.

In addition, the sheet P stored in the sheet feeding cassette 20 is fed out by the adsorbing and feeding section 12 in parallel to the toner image forming operation, and then conveyed to a registration roller 15. Next, the sheet P conveyed to the registration roller 15 is conveyed to the secondary transfer portion N2 by the registration roller 15 in synchronization with timing. Then, in the secondary transfer portion N2, the four-color toner image on the intermediate transfer belt 5 is secondarily transferred onto the conveyed sheet P by applying a positive bias to the secondary transfer roller 9. Further, after the toner image is secondarily transferred, the toner left on the intermediate transfer belt 5 is removed by a belt cleaner 11. Next, the sheet P on which the toner image is transferred is conveyed to the fixing portion 10 and heated and pressed therein, so that the full-color toner image is fixed as a permanent image, and then discharged to the outside of the printer body 100A.

Next, the sheet feeding device 200 according to this embodiment will be described using FIG. 2. As illustrated in FIG. 2, the adsorbing and feeding section 12 includes an adsorption member 29 and a holding member 24 serving as an axial holding unit which holds the adsorption member 29. Further, in FIG. 2, a sheet supporting plate 21 is provided in a housing 23 provided at the bottom surface of the printer body 100A to freely rotate in the vertical direction about a fulcrum 22. The sheet supporting plate 21 may be disposed not in the housing 23 but in the sheet feeding cassette 20.

In addition, a conveyance guide plate 40 is provided on a downstream side in a sheet feeding direction of an adsorbing and feeding section 12. Then, the center portion in a width direction perpendicular to the sheet feeding direction of the conveyance guide plate 40 is cut off, and a width L1 of the cut-off shape of the conveyance guide plate 40 is set to be larger than a width L2 of an adsorption member 29 (L1>L2). In this way, it is possible to prevent that the conveyance guide plate 40 hinders the rotation of the adsorption member 29 by setting the width L1 of the cut-off shape of the conveyance guide plate 40, when the adsorption member 29 is rotated together with a holding member 24 as described below.

The holding member 24 is disposed on the upper side at the downstream end in the sheet feeding direction of a sheet feeding cassette 20, and one end of the adsorption member 29 is fixed to the center portion in the width direction of the holding member 24. The holding member 24 is an axial member formed of a conductive material (for example, SUS303), and rotatably held by a bearing 32 provided in a printer body 100A. In addition, the holding member 24 is rotated by a driving force of a servo motor M transmitted through a drive transmission gear train G. Then, when the holding member 24 is rotated, the adsorption member 29 is also rotated integrally with the holding member 24.

A rotary encoder 31 having a function of detecting a home position of the holding member 24 is attached to one end of the holding member 24. Then, a rotation angle θ of the holding member 24 can be detected by counting the number of pulses output from an angle sensor 71 (described below) serving as a detection unit illustrated in FIG. 9 which detects the rotation of the rotary encoder 31. For example, in a case where a pulse number T0 output from the angle sensor 71 is 1000 until the holding member 24 is rotated from the home position and returns to the home position again, when the pulse number is 250, it is possible to detect that the rotation angle θ from the home position of the holding member 24 is 90°.

In addition, an insulating tape 25 is attached to one of the holding member 24 as illustrated in FIG. 3, and a power electrode 26 is formed on the insulating tape 25. Then, the power electrode 26 comes into contact with a first power brush 43 a connected to a high-voltage power source 110, and the holding member 24 comes into contact with a second power brush 43 b which is connected to a high-voltage power source 120 and applies a voltage different from the power electrode 26 to the holding member 24. With this configuration, it is possible to apply different voltages to the holding member 24 and the power electrode 26. Further, in this embodiment, the different voltages are applied to the holding member 24 and the power electrode 26 using the power brushes 43 a and 43 b, but any method of applying the power may be employed as long as the power can be applied to the rotating member.

One end of the adsorption member 29 in the sheet feeding direction is fixed to the holding member 24 as illustrated in FIG. 3, and configured in a cantilever structure. The adsorption member 29 includes a first comb-tooth electrode 30 a and a second comb-tooth electrode 30 b therein. The first and the second comb-tooth electrodes 30 a and 30 b are configured such that two electrodes in the adsorption member 29 are alternately disposed in a stripe shape, so that the power can be individually supplied to the first and the second comb-tooth electrodes 30 a and 30 b. Further, in this embodiment, the first and the second comb-tooth electrodes 30 a and 30 b are disposed to have an electrode width of 6 mm, and an electrode pitch of 2 mm.

In addition, the first comb-tooth electrode (a first electrode) 30 a as one of the two electrodes is wired to the power electrode 26, and the second comb-tooth electrode (a second electrode) 30 b as the other electrode is wired to the holding member 24. Then, in this embodiment, a negative voltage of −1 kV is applied from the high-voltage power source (a first power source) 110 to the power electrode 26 through the first power brush 43 a, and a positive voltage of 1 kV is applied from the high-voltage power source (a second power source) 120 to the holding member 24 through the second power brush 43 b.

In this way, an electrostatic adsorbing force can be applied between the surface of the adsorption member 29 as a dielectric material and the sheet by applying a positive voltage V1 one of the first and the second comb-tooth electrodes 30 a and 30 b, and a negative voltage V2 to the other one. Then, the adsorption member 29 adsorbs the sheet and holds it up by the electrostatic adsorbing force as described below. Further, the magnitude of the applying voltage is not limited as long as it causes an adsorbing force having the magnitude necessary for adsorbing the sheet to the adsorption member 29 as described below.

Further, as illustrated in FIG. 4, the adsorption member 29 is generated such that the upper surface of an insulating sheet 61 as a base material is partially cut off while not passing through the lower surface, the first and the second comb-tooth electrodes 30 a and 30 b are alternately disposed in the cut-off places, and a flexible medium resistance sheet 60 is fused thereon. Herein, in this embodiment, for example, PVDF having a volume resistivity of 1012 Ω/cm or so is employed for the medium resistance sheet 60, and a polyimide material having a volume resistivity of 1016 Ω/cm or so is employed for the insulating sheet 61. Further, the material of the adsorption member 29 may be a dielectric material, and can be preferably made using a flexible resin sheet. In addition, the adsorption member 29 may be configured such that the electrode may be disposed in the surface not the inside.

By the way, as illustrated in FIG. 3, the adsorption member 29 includes a first region 29 a serving as an adsorption portion coming into surface contact with the sheet as described below to adsorb the sheet, and a second region 29 b serving as a support portion which supports the first region 29 a and is easily bent compared to the first region 29 a. Further, the first and the second comb-tooth electrodes 30 a and 30 b are disposed in the first region 29 a.

Herein, in this embodiment, the adsorption member 29 is formed to have a small rigidity in the second region 29 b provided on a side near the holding member (one end in the sheet feeding direction) from the first region 29 a compared to the rigidity in the first region 29 a of the adsorption member 29. Then, the second region 29 b is made to be easily bent compared to the first region 29 a by setting the rigidity in the first region 29 a and the second region 29 b as described above.

Further, the rigidity of the adsorption member 29 can be evaluated by a fixed end beam on one side and a free end beam on the other end. For example, a maximum bending amount at the time when a load F is intensively applied on the free end of the beam even in a width, a thickness, and a Young's modulus is expressed by the following equation using a length l, a width b, a Young's modulus E, and a thickness h of the beam.

[Mathematical Formula 1]

In the above equation, the width b, the thickness h, and the Young's modulus E of the beam are the parameter affecting on the rigidity of the beam. Therefore, when at least one of the width b, the thickness h, and the Young's modulus E is changed, the rigidity in the first region 29 a of the adsorption member 29 can be made different from the rigidity in the second region 29 b. Herein, in this embodiment, the flexibility of the second region 29 b is realized by narrowing the width of the second region 29 b compared to the width of the first region 29 a.

Further, the area of the first region 29 a for adsorbing the sheet is determined according to an adsorption performance. For example, in the adsorption member 29 having an adsorption performance of 0.00095 N/mm2, in a case where 0.22 N is necessary for peeling off a sheet, a required area becomes 232 mm2, so that the shape of the first region 29 a is set to have an area equal to or more than the required area.

FIG. 5 is a diagram illustrating a relation between a distance from the fixed end of the adsorption member 29 and a bending amount. Further, in FIG. 5, the horizontal axis indicates the distance from the fixed end, and the vertical axis indicates the bending amount. In FIG. 5, the plotted line a indicates the adsorption member 29 having the shape illustrated in FIG. 3 according to this embodiment. The plotted line d indicates the adsorption member having an ideal shape for realizing a sheet feeding sequence of the adsorption member 29 according to this embodiment described below. The plotted line Ref indicates the adsorption member having a shape having even rigidity in the related art. Section AB corresponds to the second region 29 b, and section BC corresponds to the first region 29 a.

Herein, the ease bending is advantageous for the adsorption member 29 to enable the sheet surface to be adsorbed upward when the sheet is separated. However, when the bending amount in section BC is large, a deformation may be generated with time, and flatness of the sheet may be not secured at the time of adsorption. Therefore, an adsorption member which is easily bent in section AB as depicted with the plotted line d and hardly bent in section BC is ideal rather than an adsorption member bending in section BC as depicted by the plotted line Ref of FIG. 5.

Since the width of the second region 29 b is made narrow compared to that of the first region 29 a as described above, the adsorption member 29 depicted with the plotted line a of FIG. 5 can be formed not to be bent in section BC. Then, as the width of the second region 29 b becomes significantly different with respect to the first region 29 a, the shape approaches the ideal shape as depicted with the plotted line d of FIG. 5.

For this reason, in this embodiment, the shape of the adsorption member 29 is made as illustrated in FIG. 6. In other words, the adsorption member 29 is configured such that a total sum of the respective widths X2 and X3 of the second region 29 b of the shaped portion is set to be small compared to a width X1 of the first region 29 a (X1>X2+X3). Then, in this embodiment, a rectangular shape is employed for the first region 29 a to have a width X1 of 60 mm, a length X5 of 30 mm, and a thickness of 0.1 mm. In addition, in consideration of durability not to cause deformation, a non-adsorption portion of the second region 29 b is configured such that the width thereof is narrower than that of the first region 29 a and both portions separated into two parts are made in a rectangular shape having widths X2 and X3 of 15 mm, a length X4 of 20 mm, and a thickness of 0.1 mm.

Further, the shape of the adsorption member 29 may have the shape illustrated in (a) to (d) of FIG. 7 other than the shape described in FIG. 6. The first region of the adsorption member described in FIG. 5 is on a side denoted by A from the dotted line illustrated in FIG. 7, and the second region easily bending compared to the first region is on a side denoted by B. The adsorption member 29 illustrated in (a) of FIG. 7 is configured such that the width of the cross section of the round holes 55 in the second region becomes narrow by forming a plurality of round holes 55 as openings in the second region. In addition, the adsorption member 29 illustrated in (b) of FIG. 7 is configured such that the width of the cross section of the slits 56 in the second region becomes narrow by forming slits 56 in the second region. The adsorption member 29 illustrated in (c) of FIG. 7 has a shape provided with notches 57 in the second region, and the adsorption member 29 illustrated in (d) of FIG. 7 has a tapper shape 58 such that the width becomes narrows smoothly in the second region.

In this way, in a case where the first region and the second region are formed to have the same thickness, the first region corns to have a small volume compared to that of the second region by forming at least one of the round holes 55, the slits 56, the notches 57, and the tapper shape 58 in the second region. Herein, when the thickness is set to be equal, the volume is proportionate to the width of the adsorption member 29. Therefore, when the volume of the second region is set to be small, the width of the cross section of the second region can be made small. In other words, in this embodiment, reducing the volume of the second region means that the width of the second region becomes narrow.

FIG. 8 is a diagram illustrating a relation between the distance from the fixed end and the bending amount in the adsorption member having the shape illustrated in (a) of FIG. 6 and (a) of FIG. 7 and the adsorption member in the related art. Further, the horizontal axis of FIG. 8 indicates the distance from the fixed end, and the vertical axis indicates the bending amount. In FIG. 8, the solid line a-1 indicates the bending amount of the adsorption member 29 having the shape illustrated in FIG. 6, the solid line a-2 indicates the bending amount of the adsorption member having the shape illustrated in (a) of FIG. 7, and the line Ref indicates the bending amount of the adsorption member of the related art. In addition, in FIG. 8, section AB corresponds to the second region 29 b, and section BC corresponds to the first region 29 a.

Herein, the section formed with the holes in the second region of the adsorption member having the shape illustrated in (a) of FIG. 7 is easily bent compared to the section having no holes, as depicted by the solid line a-2 of FIG. 8, the bending property of the adsorption member having the shape illustrated in (a) of FIG. 7 is different in each section in section AB so that the solid line is not smooth. However, even though the solid line is not smooth in section AB, the bending is hardly made in section BC similarly to the solid line a-1 indicating the adsorption member having the shape illustrated in FIG. 6. Therefore, the adsorption member having the shape illustrated in (a) of FIG. 7 approaches the ideal shape as the width of a second region 55 b with respect to a first region 55 a is significantly increased similarly to the adsorption member 29 having the shape illustrated in FIG. 6. Further, the respective shapes illustrated in (b) to (d) of FIG. 7 are also formed such that the width of the second region of the adsorption member is set to be narrow compared to that of the first region similarly to (a) of FIG. 7, so that it is possible to form the shapes to approach the ideal shape of the adsorption member similarly to (a) of FIG. 7.

FIG. 9 is a control block diagram of a full-color laser beam printer according to this embodiment. In FIG. 9, a CPU 70 is illustrated as a control unit. The CPU 70 is connected to the above-mentioned image forming section 100B, the servo motor M serving as a driving unit, high-voltage power sources HV1 and HV2, the angle sensor 71 which detects the rotation angle θ of the holding member 24 by the rotary encoder 31, and an operation portion 72.

Next, a sheet separating and feeding operation of a sheet feeding device 200 according to this embodiment will be described using FIG. 10, a flowchart illustrated in FIG. 11, and a timing chart illustrated in FIG. 12. (a) of FIG. 10 is a diagram illustrating an initial state of the sheet feeding device 200. The rotation angle θ of the holding member 24 at this time is set to an initial rotation angle θ0. In the initial state, the adsorption member 29 in a non-contact state with respect to an uppermost sheet P1 among the sheets P loaded on the sheet supporting plate 21. In addition, the position of the uppermost sheet P1 is regulated by the position of the sheet supporting plate 21.

Next, when a feeding job of the sheet P starts, the CPU 70 dives the servo motor M to make the holding member 24 start to rotate from the initial state to the sheet feeding direction indicated with arrow R (S101). Further, at this time, there is no voltage application to the electrodes 30 a and 30 b as illustrated in FIG. 12. Then, the adsorption member 29 is moved toward the uppermost sheet P1 by rotating the holding member 24 in this way and comes into contact with the uppermost sheet P1 as illustrated in (b) of FIG. 10 (S102).

Thereafter, the adsorption member 29 is deformed along the uppermost sheet P1 as illustrated in (c) of FIG. 10 as the holding member 24 is rotated. Then, the adsorption member 29 is further bent by rotating the holding member 24 again from this state, and thus a surface contact area with respect to the uppermost sheet P1 is increased to enable the adsorbed sheet to be conveyed in a direction perpendicular to the surface (S103). Thereafter, when the holding member 24 continues to be rotated, the first region 29 a of the adsorption member 29 comes into sufficient contact with the uppermost sheet P1 as illustrated in (d) of FIG. 10, and the contact leading end of the first region 29 a reaches a position at a distance La from the leading end in the sheet feeding direction.

As illustrated in (d) of FIG. 10, in this embodiment, when the contact leading end of the first region 29 a reaches this position, the rotation angle θ of the holding member 24 becomes θ1. Then, when it is determined that the rotation angle θ of the holding member 24 becomes θ1 (Y of S104), the CPU 70 applies a voltage to the electrodes 30 a and 30 b in the first region as illustrated in FIG. 12 (S105). Herein, in this embodiment, when the pulse number T0 between the home positions of the rotary encoder 31 is 1000, it is determined that the rotation angle θ of the holding member 24 becomes θ1 at the time when a pulse number T1 is 500, and the voltage is applied. Further, in this embodiment, the rotary encoder 31 is used to determine whether the rotation angle θ of the holding member 24 becomes θ1, but a timer 73 or the like illustrated in FIG. 9 as described above may be used to calculate the rotation angle θ at which the rotation is stopped.

Then, when a voltage is applied to the electrodes 30 a and 30 b, a potential pattern in a stripe shape is alternately formed in the surface of the adsorption member 29 by the electrodes 30 a and 30 b and causes an electric field to generate the adsorbing force, so that the uppermost sheet P1 is adsorbed to the first region 29 a of the adsorption member 29. Herein, since the electric field is generated only in the vicinity of the surface of the adsorption member 29, the adsorbing force by the electric field works only on the uppermost sheet P1. Therefore, only the uppermost sheet P1 among the loaded sheets P is adsorbed to the adsorption member 29.

Further, (a) of FIG. 13 is a diagram for describing a state when the uppermost sheet P1 is adsorbed, and (b) of FIG. 13 is a diagram for describing a state when the uppermost sheet P1 of an adsorption member 53 having an even rigidity in the related art is adsorbed. In the adsorption member 29 of this embodiment, since the second region 29 b of the support portion is aggressively bent compared to the first region 29 a by a difference in rigidity as illustrated in (a) of FIG. 13, the second region 29 b is easily bent by the winding when the holding member 24 is rotated, and the first region 29 a is bent a little bit.

Therefore, a radius r2 of curvature at the boundary between the first region 29 a and the second region 29 b becomes smaller than the radius of curvature of the second region 29 b, so that the flatness of the first region 29 a is secured and an adsorbing area with respect to the uppermost sheet P1 can be safely secured. On the contrary, in the case of the adsorption member 53 having an even rigidity in the related art, a radius r1 of curvature at the boundary of the contact surface of the uppermost sheet P1 is large as illustrated in (b) of FIG. 13. Therefore, the flatness of the first region is not secured, and the adsorption area with respect to the uppermost sheet P1 is not safely secured. In other words, in this embodiment, since the second region 29 b is easily bent compared to the first region 29 a, the adsorption area with respect to the uppermost sheet P1 can be safely secured, and the uppermost sheet P1 can be safely adsorbed to the adsorption member 29.

In this state, when the holding member 24 is rotated, the adsorption member 29 is pulled up by the holding member 24. Then, as illustrated in (e) of FIG. 10, the adsorbed uppermost sheet P1 can be raised in the vertical direction by pulling up the adsorption member 29 so as to be separated from the sheet bundle P (S106). Thereafter, as illustrated in (f) of FIG. 10, when the rotation of the holding member 24 is progressed, the leading end of the portion Z (which has a length of La and is not adsorbed to the adsorption member 29) of the raised uppermost sheet P1 on the downstream side in the sheet feeding direction comes into contact with a conveyance guide 40 a.

Then, the uppermost sheet P1 is conveyed toward a registration roller 15 by the conveyance guide 40 a, and then engaged into the registration roller 15. Further, in this embodiment, when the uppermost sheet P1 is engaged into the registration roller 15, the rotation angle θ of the holding member 24 becomes θ2. Then, when it is determined that the rotation angle θ of the holding member 24 becomes θ2 (Y in S107), the CPU 70 stops the voltage application to the electrodes 30 a and 30 b in the first region as illustrated in FIG. 12 (S108). Further, in this embodiment, the voltage application is stopped at the time when a pulse number T2 of the rotary encoder 31 becomes 950.

In this way, the adsorption of the uppermost sheet P1 by the adsorption member 29 is released by stopping the voltage application to the electrode 30. Thereafter, as illustrated in (g) of FIG. 10, the uppermost sheet P1 is conveyed by the rotation in a direction S of the registration roller 15, and the voltage application is stopped and the adsorbing force disappears, so that the uppermost sheet P1 is separated from the adsorption member 29 (S109). Thereafter, when it is determined that a rotation position of the holding member 24 is the home position based on the pulse number of the rotary encoder 31 (Y in S110), the CPU 70 stops the servo motor M as illustrated in FIG. 12, and stops the rotation of the holding member 24 for a while (S111). Thereafter, the feeding job of the following sheet restarts (S112).

As described above, in this embodiment, the first region 29 a can be hardly bent by making the width of the second region 29 b narrower than that of the first region 29 a of the adsorption member 29 (in other words, by making the volume of the second region 29 b smaller than that of the first region 29 a). Therefore, the flatness of the first region 29 a at the time when the sheet is adsorbed can be secured, and the adsorption area required for the adsorption can be safely secured. As a result, the sheet can be separately fed with safety without causing the length of the adsorption member 29 to be increased.

In addition, in this embodiment, since the portion Z of the sheet on the downstream side in the sheet feeding direction is not adsorbed (in other words, when the sheet is adsorbed, the leading end of the sheet is not attached to the adsorption member 29), the sheet can be separated from the adsorption member 29 without a neutralization mechanism. Therefore, it is possible to reliably guide the leading end of the sheet without causing the sheet to be folded.

The description hitherto has been made about an example in which the width (volume) of the second region is made to be narrower (smaller) than the width (volume) of the first region in order to make the first region of the adsorption member hardly bent, but the invention is not limited thereto. For example, the first region of the adsorption member can be made to be hardly bent by changing the thickness or the Young's modulus of the first region and the second region of the adsorption member.

Next, the description will be made about a second embodiment according to the invention in which the first region of the adsorption member is made to be hardly bent by changing the thicknesses of the first region and the second region of the adsorption member. FIG. 14 is a diagram for describing the adsorption member of the sheet feeding device according to this embodiment. In (a) and (b) of FIG. 14, an adsorption member 51 is provided, and the adsorption member 51 includes a first region 51 a on a side coming into surface contact with the sheet and a second region 51 b on a side on the holding member. In this embodiment, the second region 51 b is made to be easily bent compared to the first region 51 a by making the thickness of the first region 51 a thicker than that of the second region 51 b.

Further, in FIG. 5 described above, the broken line b indicates the adsorption member 51 according to this embodiment. Then, with the configuration of the adsorption member 51, as illustrated in FIG. 5, the first region 51 a can be hardly bent compared to the second region 51 b in section BC. Further, as the thickness of the second region 51 b is largely different with respect to the first region 51 a, the adsorption member approaches an adsorption member d having the ideal shape indicated by the two-dotted chain line of FIG. 5. In addition, as illustrated in Equation 1 above, since a thickness is generally a parameter having much influence in a width and a thickness, the bending property of the adsorption member can approach the adsorption member d having the ideal shape by changing the thickness.

In consideration of the above description, in this embodiment, the shape of the adsorption member 51 is formed as a shape as illustrated in (a) and (b) of FIG. 14. Herein, in the adsorption member 51 illustrated in (a) of FIG. 14, a thickness T1 of the first region 51 a is configured to be thicker than a thickness T2 of the second region (T1>T2). Further, a plurality of sheets may be stacked in the first region 51 a in order to make the thickness of the first region 51 a thick. In this embodiment, two sheets which have a width of 60 mm, a length of 30 mm, and a thickness of 0.1 mm and are made of the same material as the resin sheet are stacked on the front and rear surfaces of a flexible resin sheet having a width of 60 mm, a length of 50 mm, and a thickness of 0.1 mm, so that the thickness of the first region 51 a is made to be thick.

In addition, the adsorption member 51 illustrated in (b) of FIG. 14 is configured such that the thickness T1 of the first region 51 a is thicker than the thickness T2 of the second region 51 b (T1>T2). However, in regions other than the first region 51 a, the thicknesses are intermittently different such that the thicknesses T1 and T2 are alternately disposed. In this case, similarly to the solid lines a-1 and a-1 of FIG. 8, the bending property in regions other than the first region 51 a is intermittently different, the bending is not smoothly made. However, similarly to the solid lines a-1 and a-1, even though the bending is hardly made in a first region 59 a, the adsorption member can approach an adsorption member having the ideal shape similarly to FIG. 14(a).

As described above, in this embodiment, since the thickness of the second region 51 b is made to be thinner than that of the first region 51 a of the adsorption member 51, the rigidity of the second region 51 b can be lowered compared to that of the first region 51 a, and the first region 51 a can be made hardly bent. Therefore, the flatness of the first region 51 a at the time when the sheet is adsorbed can be secured, and the adsorption area required for the adsorption can be safely secured. As a result, the sheet can be separately fed with safety without causing the length of the adsorption member 51 to be increased.

Further, in this embodiment, the thickness is changed by stacking the same two sheets on the front and rear surfaces of the flexible resin sheet, but the thickness of the sheet may be increased by coating the sheet. In addition, the material of the adsorption member 51 is not limited, and the second region may be suitably manufactured using the flexible resin sheet. In this case, the adsorption member 51 can be formed in a simply process. Further, in the adsorption member according to the first embodiment described above, the thickness of the first region 51 a may be made to be thicker than that of the second region 51 b similarly to this embodiment. In other words, this embodiment may be implemented by being combined with the first embodiment.

Next, the description will be made about a third embodiment of the invention in which the first region of the adsorption member is made to be hardly bent by changing the Young's moduli of the first region and the second region of the adsorption member. FIG. 15 is a diagram for describing the adsorption member of a sheet feeding device according to this embodiment.

In FIG. 15, an adsorption member 52 is provided, and the adsorption member 52 includes a first region 52 a on a side coming into surface contact with the sheet and a second region 52 b on a side on the holding member 24. Then, in this embodiment, by making the Young's modulus of the first region 52 a larger than that of the second region 51 b, the second region 51 b is made to be easily bent compared to the first region 51 a.

Further, in FIG. 5 described above, the broken line c indicates the adsorption member 52 according to this embodiment. Then, with the configuration of the adsorption member 52, as illustrated in FIG. 5, the adsorption member can be hardly bent in section BC compared to Ref. Further, as the Young's modulus of the second region 52 b is largely different with respect to the first region 52 a, the adsorption member approaches an adsorption member d having the ideal shape of FIG. 5. In addition, the width and the Young's modulus are parameters having the same influence on the bending property of the adsorption member in general, and the line a of FIG. 5 and the line c of FIG. 5 are plotted by the same bending graph.

In consideration of the above description, in this embodiment, the adsorption member 52 is made by selecting materials such that the material of the first region 52 a has a Young's modulus El which is larger than a Young's modulus E2 of the material of the second region. Then, the adsorption member 52 is formed by thermally fusing the selected materials having different Young's modulus.

As described above, in this embodiment, the rigidity of the second region 52 b can be lowered than that of the first region 52 a by making the Young's modulus of the second region 52 b lower than that of the first region 52 a of the adsorption member 52, and the first region 52 a can be hardly bent. Therefore, the flatness of the first region 52 a at the time when the sheet is adsorbed can be secured, and the adsorption area required for the adsorption can be safely secured. As a result, the sheet can be separately fed with safety without causing the length of the adsorption member 52 to be increased.

Further, in this embodiment, the material of the adsorption member 52 is not limited, and the adsorption member may be manufactured by suitably combining the flexible resin sheets used in the respective portions to make the Young's modulus of the second region 52 b lowered compared to that of the first region 52 a. Then, the respective regions can be given with different functions through the selection of the materials by forming the first region and the second region with the different materials.

In addition, in the adsorption member according to the first and the second embodiments described above, the Young's moduli of the first regions 29 a and 51 a may be made to be lower than those of the second regions 29 b and 51 b similarly to this embodiment. In other words, this embodiment may be implemented by being combined with the first and the second embodiments.

REFERENCE SIGNS LIST

-   12 adsorbing and feeding section -   20 sheet feeding cassette -   24 holding member -   26 power electrode -   29 adsorption member -   29 a first region -   29 b second region -   30 a first comb-tooth electrode -   30 b second comb-tooth electrode -   31 rotary encoder -   52 adsorption member -   51 a first region -   51 b second region -   52 adsorption member -   52 a first region -   52 b second region -   55 round hole -   56 slit -   57 notch -   58 tapper -   70 CPU -   71 angle sensor -   100 full-color laser beam printer -   100A full-color laser beam printer body -   100B image forming section 200 sheet feeding device -   HV1, 2 high-voltage power source -   M servo motor -   P sheet -   P1 uppermost sheet 

1. A sheet feeding device comprising: a loading portion configured to be loaded with a sheet; a rotation member configured to be disposed on an upper side of the loading portion; and an adsorption member configured to have ends and to be provided such that a part of the adsorption member is fixed to the rotation member and the sheet loaded on the loading portion is electrically adsorbed, wherein the adsorption member includes an adsorption portion which comes into contact with the sheet loaded on the loading portion, and a support portion which is provided at a position near the rotation member from the adsorption portion and has a rigidity lower than that of the adsorption portion with respect to a force applied from a sheet feeding direction.
 2. The sheet feeding device according to claim 1, further comprising: a detection unit configured to detect a rotation angle of the rotation member; a power source configured to apply a voltage to apply an adsorbing force by static electricity onto the adsorption member; and a control unit configured to apply a voltage from the power source to the adsorption member when it is determined that the adsorption portion comes into contact with the sheet based on a signal from the detection unit
 3. The sheet feeding device according to claim 1, wherein the support portion and the adsorption portion of the adsorption member are set to have the same thickness, and a volume of the adsorption member of the adsorption member is set to be smaller than that of the adsorption portion.
 4. The sheet feeding device according to claim 3, wherein at least one of a notch, a tapper, and an opening is formed in the support portion of the adsorption member so as to make the volume of the adsorption member smaller than that of the adsorption portion by the amount of the notch, the tapper, and the opening which are formed.
 5. The sheet feeding device according to claim 1, wherein a thickness of the support portion of the adsorption member is thinner than that of the adsorption portion.
 6. The sheet feeding device according to claim 1, wherein the support portion of the adsorption member is formed of a material having a Young's modulus lower than that of a material of the adsorption portion.
 7. The sheet feeding device according to claim 2, wherein the adsorption member is a dielectric having two electrodes in a surface or the inside of a flexible base material, and wherein the power source includes a first power source which applies a positive voltage to one of the two electrodes and a second power source which applies a negative voltage to the other one of the two electrodes.
 8. The sheet feeding device according to claim 7, wherein the electrode is provided in the adsorption portion.
 9. The sheet feeding device according to claim 7, wherein the rotation member is formed of a conductive material, one of the first power source and the second power source is connected to one of the two electrodes of the adsorption member through the rotation member, and the other one of the first power source and the second power source is connected to the other one of the two electrodes of the adsorption member.
 10. A sheet feeding device comprising: a loading portion configured to be loaded with a sheet; and a flexible adsorption member configured to include an adsorption portion which abuts on the sheet loaded on the loading portion from an upper side and comes into surface contact with the sheet loaded on the loading portion to adsorb the sheet by an adsorbing force by static electricity, and a non-adsorption portion which has a low rigidity compared to that of the adsorption portion.
 11. The sheet feeding device according to claim 10, further comprising a rotation member configured to be provided on the upper side of the loading portion to be rotatably in a sheet feeding direction, wherein one end of the non-adsorption portion of the adsorption member is fixed to the rotation member, and when the rotation member is rotated, the adsorption portion comes into surface contact with the sheet loaded on the loading portion to adsorb the sheet.
 12. An image forming apparatus comprising: an image forming section; a loading portion configured to be loaded with a sheet; a rotation member configured to be disposed on an upper side of the loading portion; and an adsorption member configured to have ends and to be provided such that a part of the adsorption member is fixed to the rotation member and the sheet loaded on the loading portion is electrically adsorbed, wherein the adsorption member includes an adsorption portion which comes into contact with the sheet loaded on the loading portion, and a support portion which is provided at a position near the rotation member from the adsorption portion and has a rigidity lower than that of the adsorption portion with respect to a force applied from a sheet feeding direction. 